What's the best lesson you learned in OCS/ROTC/USMA?

Don't be afraid to really delegate, or to make sure that what your subordinates understand matches what you meant to tell them.

Find smart people and keep them around you!

Don't be afraid to make a decision. Being indecisive or not making a decision is the same as Deciding to do nothing. Think through your options, use the people around you for information/input, and then make your informed decision. Too many times we'd be under pressure and it would lead to an inability to decide a course of action, and I feel that this was one of the best lessons I picked up at OCS.